Permutation: n Different Things Taken All at a Time When All Are Not Different.
The total num...
Question
The total number of 6 digited numbers greater than 400000 that can be formed by using the digits 0,2,2,4,4,5, is
A
70
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B
90
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C
100
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D
80
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Solution
The correct option is B90 400000 is a 6-digit number and the number of digits to be used is also six. Also, the numbers have to be greater than 400000, so they can begin with either 4 or 5.
Case 1: When 4 occupies the extreme left position.
Here we have to fill up the remaining 5 places with the digits 0,2,2,4,5 out of which 2 appears twice.
This can be done in 5!2!=60 ways.
Case 2: When 5 occupies the extreme left position.
Here we have to fill up the remaining 5 places with the digits 0,2,2,4,4 out of which 2 and 4 appear twice.
This can be done in 5!2!⋅2!=30 ways.
Hence, total number of required numbers is 60+30=90.